Unable to save "0" in the text field

This is working:

array(
    'name'  => 'Starting value:',
    'id' => "{$prefix}info_starting_value",
    'type'  => 'text',
    'size'  => 60,
    'std'   => "00"
)

This is NOT:

array(
    'name'  => 'Starting value:',
    'id' => "{$prefix}info_starting_value",
    'type'  => 'text',
    'size'  => 60,
    'std'   => "0"
)

Tried single quotes, no difference ;(

This code was working before the last update:
update_post_meta( $p->ID, 'cstm_info_starting_value', '0' );

Now it's not working. I am using Meta Box version 4.7.2

I am using CRON to reset values for many records on a daily basis and now it's not working for some reason.

Could you tell me any quick fix how to save a zero into a text field in Meta Box? std is not as important, but update_post_meta is. I have tried this:

$zero = "0"; update_post_meta( $p->ID, 'cstm_info_starting_value', $zero );

But it doesn't work, but this worked:

$zero = "00"; update_post_meta( $p->ID, 'cstm_info_starting_value', $zero );

But I need 0 and not 00 saved in the db for that field.

Thanks for the info how to solve this problem.